1. Field of the Invention
The present invention relates to a hydraulic brake apparatus for supplying hydraulic brake pressure to each wheel brake cylinder operatively mounted on each wheel of a vehicle, and more particularly to the apparatus for advancing a master piston by means of a hydraulic boosting device having a pressure regulating valve.
2. Description of the Related Arts
Heretofore, there is known a hydraulic brake apparatus which is provided with a hydraulic boosting device having a pressure regulating valve for regulating hydraulic pressure of a hydraulic pressure source, and adapted to advance a master piston in response to output of the device, so as to discharge hydraulic braking pressure from a master chamber. For example, a brake pressure generating device for a vehicle is disclosed in the U.S. Pat. No. 5,515,678, which corresponds to Japanese Patent Laid-open publication No.7-172291. In this publication, it is described that hydraulic pressure regulated by a spool valve is transmitted to an auxiliary pressure chamber so as to boost up the operation a first piston, as disclosed in FIG. 1 of the patent.
According to the apparatus which is provided with the hydraulic boosting device having the pressure regulating valve for regulating the hydraulic pressure of the hydraulic pressure source in response to braking operation of a vehicle driver and discharging it, and adapted to apply the boosting force to the master piston, as disclosed in the publication, a sufficiently large capacity has to be provided for the master chamber, so that it is difficult to reduce the size of the apparatus. Therefore, it has been proposed to form the pressure regulating valve separately from the apparatus and provide it in parallel with the master cylinder, so as to reduce its length in the axial direction, for example. However, it is still difficult to reduce the size of the apparatus as a whole.
In accordance with a recent progress in electronics, it has been proposed to provide braking force with a combination of electronic means and hydraulic means, and provide a brake feeling to a vehicle driver in response to his braking operation, through a simulator, whereby the size of the apparatus can be reduced. According to this apparatus, however, it is not so easy to provide the brake feeling to the vehicle driver in response to a stroke of braking operation, and provide the brake feeling in response to depressed force to a brake pedal, appropriately. As a result, a complicated control apparatus will be required. When a vehicle deceleration is low, for example, it is desirable to provide the brake feeling in response to the stroke of braking operation, to increase the braking force in accordance with the stroke of the brake pedal. Thereafter, it is desirable to provide the brake feeling in response to the depressed force, without any stroke of the brake pedal, thereby to provide a rather rigid brake feeling.